1. Field of the Invention
The present invention relates to a dynamic bearing device, which rotatably supports an axial member in a non-contact manner by an dynamic pressure action of a lubricating oil generated in a bearing gap, a producing method thereof, and a motor using the same. This bearing device is suitable for use in information-processing equipment, including the spindle motors for magnetic disk devices such as HDD and FDD, optical disk devices for CD-ROM, CD-R/RW, DVD-ROM/RAM, etc. and magneto-optical disk devices for MD, MO, etc., the polygon scanner motors in laser beam printers (LBP), or as small-scale motors for electrical equipment such as axial flow fans.
2. Description of the Related Art
In various types of the motor described above, performances such as increased speed, lower costs, and lower noise generation, in addition to high rotational precision, are required. One of the structural elements that determine these performance requirements is the bearing that supports the spindle of the motor. In recent years, dynamic bearings, which are superior in the above performance requirements, have been investigated, or actually uses, as this kind of bearing.
For example, a dynamic bearing device installed in a spindle motor of a disk drive device, such as HDD, is provided with a radial bearing portion, which rotatably supports an axial member in a non-contact manner in the radial direction, and a thrust bearing portion, which rotatably supports the axial member in a non-contact manner in the thrust direction. The radial bearing portion is constituted with a dynamic bearing, in which grooves for generating the dynamic pressure (dynamic pressure generating grooves) are provided in either an inner peripheral surface of a bearing sleeve or an outer peripheral surface of the axial member. The thrust bearing portion is constituted, for example, with a dynamic bearing, in which dynamic pressure generating grooves are provided in either both end surfaces of a flange portion of the axial member or in the surfaces opposing these end surfaces (such as an end surface of the bearing sleeve, or an end surface of a thrust member fixed to a housing) (for an example, see Japanese Patent Laid-Open Publication No. 2002-061641).
Normally, the bearing sleeve is fixed to an inner periphery of the housing, and the thrust member is fixed to the inner periphery at one end of the housing. Furthermore, in order to prevent the lubricating oil, which is filled into an internal space within the housing, from leaking out, a seal portion is often provided at the other end of the housing.
In the dynamic bearing device described above, press fitting is sometimes used as a means for fixing the thrust member to the inner periphery at one end of the housing. In addition, after press fitting the thrust member, an adhesive is sometimes filled into the press fitted portion from outside the housing, thereby sealing the press fitted portion with adhesive. However, accompanying the press fitting process, a predetermined region of the outer periphery of the housing undergoes expansion deformation outward, which might give rise to the following problems.
For example, when this kind of dynamic bearing device is used for the rotation support of any of the motors described above, the outer periphery of the housing is usually secured closely to the inner periphery of a bracket (a retaining member) with an adhesive, and the dimensions in an axial direction and the gap in which the adhesive is filled of the bonded portions of the two members are determined with due consideration to the adhesive strength that can be achieved. However, if during the press fitting of the thrust member, a portion of the bonding surface (securing surface) of the outer periphery of the housing undergoes expansion deformation, when securing the bearing device to the inner periphery of the retaining member, the gap in which the adhesive is filled becomes non-uniform in the axial direction, which leads to concerns over potential decreases in adhesive strength, and the potential occurrence of resonance problems.
Furthermore, securing the outer periphery of the housing closely to the inner periphery of the bracket (retaining member) via press fitting is another possibility, although in a similar manner to above, if during the press fitting of the thrust member, a portion of the press fitting surface (securing surface) of the outer periphery of the housing undergoes expansion deformation, when press fitting the bearing device to the inner periphery of the retaining member, the interference therebetween is non-uniform in an axial direction, which leads to concerns over potential decreases in the press fitting strength, and the potential occurrence of resonance problems.
Furthermore, when press fitting is employed as a means for securing the thrust member, the following problems might arise.
Namely, each of the structural components of the dynamic bearing device is cleaned following manufacture to remove any fine metallic particles such as cutting leavings generated during processing of the component, however, during press fitting of the thrust member, fine metallic particles such as abrasion particles (hereafter referred to as “abrasion particles”) might be generated due to the sliding friction between the outer peripheral portion of the thrust member and the inner peripheral portion at one end of the housing to penetrate into the housing. Any abrasion particles penetrating into the housing will invade the bearing portion among the lubricating oil to exercise an unfavorable influence on the performance or the life of the bearing.
Furthermore, in the dynamic bearing device as described above, an adhesive is often used as a means for fixing the bearing sleeve to the housing. In such cases, for example, an adhesive is applied, in advance, to the inner peripheral surface of the housing, and the bearing sleeve is then inserted inside the housing and positioned at a predetermined location, thereafter, the adhesive is hardened. However, depending on the quantity of adhesive that is applied, during the insertion of the bearing sleeve inside the housing and the movement of the bearing sleeve to the predetermined location, excess adhesive may go round to the front of the bearing sleeve as it moves to exercise an unfavorable influence on the positioning of the bearing sleeve or the performance of the bearing.
For example, in the dynamic bearing device disclosed in Japanese Patent Laid-Open Publication No. 2002-061641, positioning of the bearing sleeve relative to the housing is achieved by contacting one end surface of the bearing sleeve with the inside surface of a seal portion (collar portion) provided at one end of the housing, however, if the go round of the excess adhesive takes place, when the bearing sleeve is moved to its final position, the adhesive will be trapped between the one end surface of the bearing sleeve and the inside surface of the seal portion, so that the precise positioning of the bearing sleeve relative to the housing may not be achieved.
Furthermore, the applicant of the present application has already filed an application (Japanese Patent Application No. 2002-117297) relating to a dynamic bearing device wherein longitudinal grooves are formed in the outer peripheral surface of the bearing sleeve, and lateral grooves that connect the longitudinal grooves with the inner peripheral surface of the bearing sleeve are formed in the end surface at one end of the bearing sleeve, thereby forming a circulation channel for a lubricating oil filled in an internal space within the housing. In this dynamic bearing device, however, the go round of the excess adhesive may cause the lateral grooves to be blocked with adhesive.